1. Macro Cellular Wireless Networks
Many people use mobile stations (e.g. cell phones and personal digital assistants (PDAs)) to communicate with macro cellular-wireless networks (i.e. wireless wide area networks (WWANs)), which typically provide communication services such as voice, text messaging, and packet-data communication. These mobile stations (i.e. access terminals) and networks typically communicate with each other over a radio-frequency (RF) air interface according to a wireless-communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1×RTT networks” (or “1× networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Recently, service providers have introduced mobile stations and wireless networks that communicate using a CDMA protocol known as EV-DO, which stands for “Evolution Data Optimized.” EV-DO networks, operating in conformance with one or more releases and/or revisions of industry specification IS-856, both Release 0 and Revision A thereof being hereby incorporated herein by reference, provide high-rate packet-data service (including Voice over IP (VoIP) service) to mobile stations using a combination of time-division multiplexing (TDM) on the forward link (from the network to mobile stations) and CDMA technology on the reverse link (from mobile stations to the network). Furthermore, some “hybrid” mobile stations can communicate with both 1× networks and EV-DO networks.
Mobile stations typically conduct wireless communications with these networks via one or more base transceiver stations (BTSs), each of which send communications to and receive communications from mobile stations over the air interface. Each BTS is in turn connected with a network entity known as a base station controller (BSC) (i.e. radio network controller (RNC)), which controls one or more BTSs and acts as a conduit between the one or more BTSs and one or more switches or gateways, such as a mobile switching center (MSC) and/or a packet data serving node (PDSN). The one or more switches or gateways may then interface with one or more signaling and/or transport networks. As examples, an MSC may interface with the public switched telephone network (PSTN), while a PDSN may interface with one or more core packet data networks and/or the Internet. As such, mobile stations can typically communicate over the one or more signaling and/or transport networks from anywhere inside the coverage area of one or more BTSs, via the BTS(s), a BSC, and a switch or gateway such as an MSC and/or PDSN.
The base stations (i.e. BTSs or combinations of (1) one or more BTSs and (2) a BSC) for these macro cellular networks are typically not associated with any subscriber or small group of subscribers in particular; rather, they are placed in publicly-accessible locations and are used by the service provider's customers generally. These base stations collectively blanket cities, rural areas, etc. with coverage; as such, they are referred to generally and herein as macro (or macro-network) base stations, and the network they collectively form—or to which they collectively belong—is referred to generally and herein as the macro network. And the BTSs associated with macro networks may be referred to herein as macro BTSs (or just BTSs).
Mobile stations and macro base stations conduct communication sessions (e.g. voice calls and data sessions) over frequencies known as carriers (i.e. macro carriers), each of which may actually be a pair of frequencies, with the base station transmitting to the mobile station on one of the frequencies, and the mobile station transmitting to the base station on the other. This approach is known as frequency division duplex (FDD). And the base-station-to-mobile-station link is known as the forward link, while the mobile-station-to-base-station link is known as the reverse link. Note that an instance of a carrier in a macro coverage area referred to as a sector may be known and referred to herein as a sector-carrier or macro sector-carrier.
When a mobile station seeks to originate a communication session (e.g. a voice call) with, or respond to a page message from, a base station such as a macro network base station or a smaller base station known as a femtocell (described more fully below), the mobile station sends one or more messages known as access probes to the base station over a reverse-link access channel. Typically, the mobile station will send an initial access probe at a default power level, and then send successive access probes at increased power levels until acknowledged by the base station.
2. Reverse-Link Conditions
At a given moment, the sum total of what a macro base station is receiving on a given sector-carrier is known as the reverse noise on that sector-carrier. A macro base station, along with or in addition to other macro-network entities, may detect and track reverse noise on the macro network. A macro base station may also broadcast (to mobile stations) messages that include information on reverse noise conditions. For instance, a macro base station may suggest a power level for mobile stations to use for transmissions on the reverse link of the macro network, such that the suggested power level is appropriate in the face of the current reverse noise conditions of the macro network.
a. Reverse Noise Rise
At regular intervals, and in fact quite frequently (e.g., once for every forward-link timeslot (i.e. once every approximately 1.67 ms)), macro base stations compute reverse noise rise (RNR), which is the difference between (i) the reverse noise that the macro base station is currently detecting and (ii) a baseline level of reverse noise. Thus, the macro base station computes how far the reverse noise has risen above that baseline.
To determine the baseline, EV-DO networks, as one example, typically periodically utilize what is known as a silent interval, which may occur on the order of once every five minutes, and last on the order of 40-100 ms, both of which are typically configurable. During the silent interval, mobile stations know not to transmit anything to the macro base station. The macro base station can then measure whatever else is out there. As such, the baseline corresponds to the amount of reverse noise when the sector-carrier is unloaded (i.e. without any transmitting mobile stations). And other reverse-link-noise levels, such as 24-hour or other minimums, could be used as a baseline.
In general, the lower the RNR is at a given moment, the more favorable the RF conditions are for communication between mobile stations and a macro base station at that moment. Correspondingly, the higher the RNR, the less favorable the RF conditions are. Moreover, a low RNR generally corresponds to a sector-carrier being lightly loaded, in other words that is supporting communications for a relatively low number of mobile stations. A high RNR, as one might expect, generally corresponds to a sector-carrier being heavily loaded, in other words that is supporting communications for a relatively high number of mobile stations. A macro base station may include the RNR in signaling messages sent to mobile stations.
b. Reverse Activity Bit (RAB)
In EV-DO networks, macro base stations typically use the calculated value of RNR to, among other things, set or clear what is known as the Reverse Activity Bit (RAB), which is a value that the macro base station makes equal to 0 or 1, and repeatedly transmits to all the mobile stations operating on a given sector-carrier. Note that making the RAB equal to 0 is known as “clearing” the RAB, while making the RAB equal to 1 is known as “setting” the RAB. As stated, the macro base station typically calculates RNR at the same frequency at which it transmits forward-link timeslots, or once every 1.67 ms. The macro base station typically sets or clears the RAB at this same frequency.
With respect to how the macro base station chooses whether to set or clear the RAB, if the RNR is above a threshold (“RNR threshold” or “RAB threshold”), which is a configurable parameter that may be between 0 dB and 30 dB, the macro base station sets the RAB. If the RNR is below the RNR threshold, the macro base station clears the RAB. The macro base station transmits the RAB in a TDM channel—known as the reverse-activity channel—on the forward link. That channel is itself a TDM portion of a forward-link channel known as the Media Access Control (MAC) channel.
c. Reverse-Link Frame Error Rate (RFER)
The reverse-link frame error rate (RFER) is another mechanism by which macro base stations can detect and track reverse noise. Using 1× networks by example, data is transmitted on the air interface in units known as frames, which typically last 20 ms. Some reverse-link frames received by the macro base station contain no errors, while some frames do contain errors as a result of imperfect transfer from the mobile station, and some are not received at all. The RFER, then, is a ratio, computed per mobile station by the macro base station over a given time period of (i) the number of error-containing and missing frames from each mobile station to (ii) the total number of frames that the macro base station should receive from that respective mobile station. Other things being more or less equal, the more power the mobile station uses to transmit to the base station, the lower the mobile station's RFER will be.
At approximately the same frequency at which the macro base station is receiving reverse-link frames (i.e., once every 20 ms) from a mobile station, the macro base station computes a RFER for that mobile station over some previous number of frames, e.g., 20, 100, 200, etc. Thus, on a frame-by-frame basis, the macro base station computes a RFER for some rolling window of previous frames.
3. Femtocells
Many macro-network subscribers, including private consumers and small businesses, among others, in addition to having wireless service (which may include data service) for their respective mobile stations, also have high-speed (a.k.a. broadband) Internet access through another communication channel, which may be cable-modem service, digital-subscriber-line (DSL) service, satellite-based Internet service, and/or some other option or combination thereof.
In a typical arrangement, a user may have a cable modem connected (a) via coaxial cable to a cable provider's network and (b) via Ethernet cable to a wireless (e.g. IEEE 802.11 (Wi-Fi)) router. That router may include one or more Ethernet ports to which computers or other devices may be connected, and may also include wireless-access-point functionality, providing a wireless packet-data interface to, e.g., laptop computers, digital video recorders (DVRs), appliances, and/or any other computing devices or their respective wireless network adapters.
To address gaps in macro-network coverage (e.g. in buildings) and for other reasons, macro-network service providers offer consumers devices referred to herein as femtocells, which may also be referred to as femto base stations, femto BTSs, picocells, pico base stations, pico BTSs, microcells, micro base stations, micro BTSs, and by other names, such as Internet base stations or perhaps low-cost Internet base stations (LCIBs). Note that the aforementioned terms that end in “cell” may also be used generally and herein to refer to the coverage area provided by the respective device. And with respect to the term LCIB, low-cost is not used as a limiting term; that is, devices of any monetary cost may be categorized as LCIBs, though most LCIBs typically will be less expensive on average than most macro-network base stations.
A femtocell may be approximately the size of a desktop phone or Wi-Fi access point, and is essentially a low-power, low-capacity version of a macro base station. Thus, a femtocell may use a power outlet, perhaps with a transformer providing a DC power supply. The femtocell may have a wired (e.g. Ethernet) or wireless (e.g. Wi-Fi) connection with the user's router, and would thus have connectivity to the Internet and/or one or more other packet-data networks via that broadband connection. A femtocell may establish a virtual-private-network (VPN) connection over the Internet with an entity (e.g. a VPN terminator) on the wireless-service (macro-network) provider's core network, and thereby be able to securely communicate via the VPN terminator with other entities on that core network and beyond.
A typical femtocell also has a wireless-communication interface (operating according to, CDMA, EV-DO, and/or one or more other protocols) that is compatible with the user's mobile station(s), such that the femtocell may act as a micro base station, providing coverage for the mobile station(s) on the macro-network provider's network via the user's Internet connection. Usually, a femtocell provides service on a single RF carrier (or on a single carrier per protocol, if multiple protocols (e.g. CDMA and EV-DO) are supported), and transmits what is known as and referred to herein as a pilot beacon, which is a radio beacon that includes overhead messages and parameters that mobile stations use to connect with (i.e. handoff to) the femtocell.